As shown in FIG. 1, a common computer system (100) includes a central processing unit (CPU) (102), memory (104), and numerous other elements and functionalities typical of today's computers (not shown). The computer (100) may also include input means, such as a keyboard (106), a mouse (108), and an output device, such as a monitor (110). Those skilled in the art will understand that these input and output means may take other forms in an accessible environment. In one or more embodiments of the invention, the computer system may have multiple processors and may be configured to handle multiple tasks.
The CPU (102) is an integrated circuit (IC) and is one of many integrated circuits included in the computer (100). Integrated circuits may perform operations on data and transmit resulting data to other integrated circuits. The performance of the computer depends heavily on the speed and efficiency with which data is transmitted between integrated circuits.
FIG. 2 shows a block diagram of a prior art system (200) for transmitting data from a transmitting IC (202) to a receiving IC (250) using a transmission path (248). A data source (210) represents computing elements of the transmitting IC (202). The data source (210) may produce data for the transmitting IC (202) to transmit to the receiving IC (250). Data to be transmitted is sent by the data source (210) to the transmitting output buffer (212) to be put onto the transmission path (248). The transmission path (248) propagates the data signal to the receiving IC (250) where the data signal is received at the data destination (262), which represents the receiving IC's (250) input buffer and computing elements.
The rate of data transmission on the transmission path (248) between the transmitting IC (202) and the receiving IC (250) on a printed circuit board (PCB) is limited by a bandwidth of the transmission path (248). However, the rate at which data can be put onto the transmission path (248) is limited by the speed at which output buffer (212) on the transmitting IC (202) can operate. Using current technologies, the rate at which data can be put onto the transmission path (248) may be substantially lower than the rate at which the transmission path (248) may transmit.
If the output buffer (212) is incapable of using the entire bandwidth of the transmission path (248), then part of the bandwidth of the transmission path (248) is wasted. In order to transmit more data, more transmission paths (like 248) must be used. Additional transmission paths result in increased cost of materials and increased design complexity. Each of the added transmission paths must also use a package pin to drive the data signals on those transmission paths, increasing complexity and cost still more.
Printed circuit boards are commonly constructed from a glass fiber epoxy laminate called FR4. Transmission paths are traces of metal on the PCB. The traces of metal form wires along which electrical signals may be propagated. The traces of metal are commonly constructed from copper. One of ordinary skill in the art will understand that materials other than FR4 may be used for the PCB and that materials other than copper may be used for the metal traces. Properties of the metal traces and of the PCB material determine the bandwidth of the transmission path formed by the metal traces on the PCB. A significant property of the metal traces is resistivity, which, along with geometry, determines the resistance of the traces. A significant property of the PCB material is the dielectric constant, which, along with geometry, determines the capacitance between metal traces.
A PCB may connect to another PCB through a PCB connector. A PCB connector may include multiple conductive elements to connect multiple metal traces on a first PCB to multiple metal traces on a second PCB. A transmission path may traverse a metal trace on a first PCB, a PCB connector, and a metal trace on a second PCB.